DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage. Chevrolet PJJ 2000

For 1990-2009 cars
Engine Controls Components
Engine Data Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The Engine Coolant Temperature (ECT) sensor uses a thermistor in order to control the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a voltage on the signal circuit to the sensor. When the engine is cold, the sensor resistance is high, therefore, the ECT signal voltage will be high.

As the engine warms, the sensor resistance becomes less and the voltage drops. At the normal engine operating temperature, the voltage will be between 1.5 and 2.0 volts at the ECT signal terminal.

The ECT sensor controls the following items:

• | The fuel delivery

• | The Torque Converter Clutch (TCC)

• | The Ignition Control (IC)

• | The Evaporative Emission (EVAP) canister purge valve

• | The Idle Air Control (IAC) valve

• | The Electric cooling fan

### Conditions For Running The DTC

The engine run time is more than 60 seconds.

### Conditions for Setting the DTC

The ECT sensor indicates that the engine coolant temperature is less than -40°C (-40°F) for 6.25 seconds.

### Action Taken When the DTC Sets

• | The Malfunction Indicator Lamp (MIL) will illuminate. after two consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.

• | A history DTC stores.

• | The coolant fan turns ON.

• | The PCM will default to 20°C (68°F) for the first 60 seconds of the engine run time and then to 92°C (198°F).

### Conditions for Clearing the MIL/DTC

• | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

• | A history DTC will clear after 40 consecutive warm up cycles without a fault.

• | Use a scan tool to clear the DTCs.

### Diagnostic Aids

• | The normal operating temperature for the engine cooling system is between 90°C (194°F) and 95°C (203°F).

• | Use the Temperature vs. Resistance table in order to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance .

### Test Description

The numbers below refer to the step numbers on the diagnostic table:

1. Verifies that the fault is present.

2. If DTC P0118 can be repeated only by duplicating the Fail Records conditions, refer to the Temperature vs. Resistance table. The table may be used to test the ECT sensor at various temperatures to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the ECT sensor. If the ECT sensor appears to be OK, the fault is intermittent; refer to Diagnostic Aids.

3. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.

#### DTC P0118 - ECT Sensor Circuit High Voltage

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check

2

1. Turn ON the ignition.
2. With a scan tool, observe the Eng. Cool. Temp. parameter.

Does Eng. Cool. Temp. value measure less than the specified value?

-38°C (-36°F)

Go to Step 4

Go to Step 3

3

1. Turn ON the ignition, with the engine OFF.
2. With a scan tool, review and record Fail Records.
3. Operate vehicle within Fail Records conditions.

Did the DTC failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

1. Turn OFF the ignition.
2. Disconnect the PCM and the ECT sensor.
3. Turn ON the ignition.
4. Test the ECT sensor signal circuit for a short to voltage. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 5

5

1. Turn OFF the ignition.
2. Reconnect the PCM.
3. Jumper the ECT signal circuit and the sensor ground circuit together at the ECT sensor.
4. Turn ON the ignition, with the engine OFF.
5. Observe ECT parameter with a scan tool.

Does the ECT value measure at the specified value?

140°C (284°F)

Go to Step 7

Go to Step 6

6

1. Jumper the ECT signal circuit at the ECT harness connector to a good ground.
2. Observe the Eng. Cool. Temp. parameter with a scan tool.

Does the Eng. Cool. Temp. value measure at the specified value?

140°C (284°F)

Go to Step 8

Go to Step 9

7 | Inspect for poor connections at the ECT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11

8

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Test the ECT sensor ground circuit for an open. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

9

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Test the ECT signal circuit for an open. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

10 | Inspect for a poor sensor ground or ECT signal circuit connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12
11 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement Did you complete the replacement? | -- | Go to Step 13 | --
12 | Important: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming Replace the PCM. Did you complete the replacement? | -- | Go to Step 13 | --

13

1. Use the scan tool in order to clear DTCs.
2. Operate the vehicle within the Fail Record conditions.

Does the DTC reset?

--

Go to Step 2

System OK